A large number of processes have been described for converting starch to starch hydrolysates, such as maltose, glucose or specialty syrups, either for use as sweeteners or as precursors for other saccharides such as fructose. Glucose may also be fermented to ethanol or other fermentation products.
Starch is a high molecular-weight polymer consisting of chains of glucose units. It usually consists of about 80% amylopectin and 20% amylose. Amylopectin is a branched polysaccharide in which linear chains of alpha-1,4 D-glucose residues are joined by alpha-1,6 glucosidic linkages.
Amylose is a linear polysaccharide built up of D-glucopyranose units linked together by alpha-1,4 glucosidic linkages. In the case of converting starch into a soluble starch hydrolysate, the starch is depolymerized. The conventional depolymerization process consists of a gelatinization step and two consecutive process steps, namely a liquefaction process and a saccharification process. Granular starch consists of microscopic granules, which are insoluble in water at room temperature. When an aqueous starch slurry is heated, the granules swell and eventually burst, dispersing the starch molecules into the solution. During this “gelatinization” process there is a dramatic increase in viscosity. As the solids level is 30-40% in a typical industrial process, the starch has to be thinned or “liquefied” so that it can be handled. This reduction in viscosity is today mostly obtained by enzymatic degradation.
HFCS is manufactured from high DX syrups, the term DX meaning percentage by weight of of dextrose (D-glucose) calculated on the basis of dry substance (DS) of syrup. The overall enzymatic process generally adopted for conversion of starch into high DX syrup is a two-stage process. The first step is the liquefaction, wherein the long-chained starch is degraded into smaller branched and linear units (maltodextrins) by an alpha-amylase. The liquefaction process is typically carried out at about 105-110° C. for about 5 to 10 minutes followed by about 1-2 hours at about 95° C. The temperature is then lowered to 60° C., a glucoamylase or a beta-amylase and optionally a debranching enzyme, such as an isoamylase or a pullulanase are added, and the saccharification process proceeds for about 24 to 72 hours.
WO 2013/057141 and WO 2013/057143 describe alpha-amylase variants and uses thereof in, e.g., starch processing, production of fermentation products, processes for producing fermentation products from ungelatinized starch-containing material, and processes for producing fermentation products from gelatinized starch-containing material. These variants are described as having, e.g., increased stability when incubated at low pH and/or at high temperature, in particular at low calcium concentrations, and in particular in the presence of at least 0.1% starch, e.g., in the presence of 0.9% or 1% starch.
There remains a need for improvement of processes for producing sugars and syrups.